Load impedance decision device, wireless power transmission device, and wireless power transmission method

ABSTRACT

A load impedance decision device, a wireless power transmission device, and a wireless power transmission method are provided. At least one of a distance and an angle between two resonators may be measured. A load impedance may be determined based on at least one of the measured distance and the measured angle. When the distance between the two resonators changes, a high power transfer efficiency may be maintained without using a separate matching circuit. Where the load impedance is determined, a test power may be transmitted. Depending on a power transfer efficiency of the test power, the load impedance may be controlled and power may be wirelessly transmitted from the source resonator to the target resonator.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 10-2009-0107508, filed on Nov. 9, 2009, in theKorean Intellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND

1. Field

The following description relates to a load impedance decision device, awireless power transmission device, and a wireless power transmissionmethod, and more particularly, to a wireless transmission technologythat efficiently manages wireless power transmission from a sourceresonator to a target resonator even if the distance between the sourceresonator and the target resonator changes.

2. Description of Related Art

With the development of information technology (IT), an increasingamount of portable electronic devices are being distributed. Due tovarious characteristics of the portable electronic products, a batteryperformance of a corresponding portable electronic product becomes animportant issue. Various portable electronic products and homeelectronic appliances have the ability to transmit data wirelessly,however, the portable electronic products typically receive power usinga wired connection such as plugging the device into an outlet.

Currently, researches are conducted on a wireless power transmissiontechnology that may wirelessly supply power. Due to characteristics ofwireless environments, a distance between a source resonator and atarget resonator may vary over time and a matching condition between thesource resonator and the target resonator may also vary. Accordingly,disclosed is a new scheme that may enhance the efficiency of a wirelesstransmission even in environments where the source resonator and/ortarget resonator dynamically change location.

SUMMARY

In one general aspect, there is provided a load impedance decisiondevice comprising a measurement unit to measure at least one of adistance and an angle between a source resonator and a target resonator,and a decision unit to determine the load impedance based on at leastone of the measured distance and the measured angle.

The decision unit may determine the load impedance based on both themeasured distance and the measured angle.

The load impedance decision unit may be included in the sourceresonator, and the measured angle may correspond to an angle with whichthe source resonator is tilted with respect to the target resonator.

In another aspect, there is provided a wireless power transmissiondevice comprising a load impedance decision unit, and a change unit tochange an impedance of the wireless power transmission device to beconjugated with a load impedance determined by the load impedancedecision unit, wherein the load impedance decision unit comprises ameasurement unit to measure at least one of a distance and an anglebetween the wireless power transmission device and a target resonator,and a decision unit to determine the load impedance based on at leastone of the measured distance and the measured angle.

The wireless power transmission device may further comprise atransmitter to transmit, to a terminal, information associated with theload impedance determined by the load impedance decision unit.

The change unit may change the impedance of the wireless powertransmission device based on at least one of a tunable resistance, aninductor, and a capacitor.

The wireless power transmission device may further comprise a testingunit to transmit a test power using the changed impedance, and a controlunit to control the load impedance decision unit to re-determine theload impedance when a power transfer efficiency of the test power isless than a reference value, and to control the wireless powertransmission device to wirelessly transmit a power using the changedimpedance when the power transfer efficiency of the test power isgreater than or equal to the reference value.

The decision unit may determine the load impedance based on both themeasured distance and the measured angle.

The wireless power transmission device may include a source resonator,and the measured angle may correspond to an angle with which the sourceresonator is tilted with respect to the target resonator.

In another aspect, there is provided a terminal to wirelessly receivepower, comprising a load impedance decision unit, and a change unit tochange an impedance of the terminal to match a load impedance determinedby the load impedance decision unit, wherein the load impedance decisionunit comprises a measurement unit to measure at least one of a distanceand an angle between the terminal and a target resonator, and a decisionunit to determine the load impedance based on at least one of themeasured distance and the measured angle.

The terminal may further comprise a transmitter to transmit, to awireless power transmission device, information associated with the loadimpedance determined by the load impedance decision unit.

The change unit may change the impedance of the terminal based on atleast one of a tunable resistance, an inductor, and a capacitor.

The terminal may further comprise a signal transmitter to transmit atest power request signal to a wireless power transmission device whenthe change unit changes the impedance of the terminal, and a controlunit to control the load impedance decision unit to re-determine theload impedance when a power transfer efficiency of the test power isless than a reference value, and to transmit a signal to the wirelesspower transmission device to wirelessly transmit power when the powertransfer efficiency of the test power is greater than or equal to thereference value.

The decision unit may determine the load impedance based on both themeasured distance and the measured angle.

The terminal may include a source resonator, and the measured angle maycorrespond to an angle with which the source resonator is tilted withrespect to the target resonator.

In another aspect, there is provided a method to determine a loadimpedance, comprising measuring at least one of a distance and an anglebetween a source resonator and a target resonator, and determining theload impedance based on at least one of the measured distance and themeasured angle.

The load impedance may be determined based on both the measured distanceand the measured angle.

The measured angle may correspond to an angle with which the sourceresonator is tilted with respect to the target resonator.

In another aspect, there is provided a method to wirelessly transmit apower, comprising determining a load impedance, and changing animpedance to be conjugated with the determined load impedance, whereinthe determining comprises measuring at least one of a distance and anangle between a source resonator and a target resonator, and determiningthe load impedance based on at least one of the measured distance andthe measured angle.

Other features and aspects may be apparent from the followingdescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless powertransmission device that transmits power wirelessly to a terminal.

FIG. 2 is a diagram illustrating an example of a load impedance decisiondevice.

FIG. 3 is a diagram illustrating an example of a Z-matrix of a loadimpedance, a source resonator, and a target resonator.

FIG. 4 is a diagram illustrating an example of a wireless powertransmission device.

FIG. 5 is a diagram illustrating an example of a terminal thatwirelessly receives power.

FIG. 6 is a flowchart illustrating an example of a method fordetermining a load impedance.

FIG. 7 is a flowchart illustrating an example of a method for wirelesslytransmitting power.

Throughout the drawings and the description, unless otherwise described,the same drawing reference numerals should be understood to refer to thesame elements, features, and structures. The relative size and depictionof these elements may be exaggerated for clarity, illustration, andconvenience.

DESCRIPTION

The following description is provided to assist the reader in gaining acomprehensive understanding of the methods, apparatuses, and/or systemsdescribed herein. Accordingly, various changes, modifications, andequivalents of the methods, apparatuses, and/or systems described hereinmay be suggested to those of ordinary skill in the art. Also,description of well-known functions and constructions may be omitted forincreased clarity and conciseness.

FIG. 1 illustrates an example of a wireless power transmission devicethat transmits power wirelessly to a terminal.

Referring to FIG. 1, wireless power transmission device 110 wirelesslytransmits power to terminal 120. In this example, the wireless powertransmission device 110 includes a source resonator 111, and theterminal 120 includes a target resonator 121. As an example, thewireless power transmission device 110 may be included in a portabledevice.

FIG. 2 illustrates an example of a load impedance decision device.

Referring to FIG. 2, load impedance decision device 200 includes ameasurement unit 201 and a decision unit 202. The measurement unit 201may measure at least one of a distance d 211 and an angle θ 212 betweena source resonator 210 and a target resonator 220. For example, themeasurement unit 201 may include a distance sensor (not shown) that useslight waves and/or ultrasonic waves. The measurement unit 201 maymeasure the distance d 211 using the distance sensor. The measured angleθ 212 may indicate an angle at which the target resonator 220 is tiltedwith respect to the source resonator 210.

The decision unit 202 may determine a load impedance based on at leastone of the measured distance d 211 and angle θ 212. For example, thedecision unit 202 may determine the load impedance based on the measureddistance d 211. The decision unit may determine the load impedance basedon the angle θ 212. As another example, the decision unit 202 maydetermine the load impedance based on both the measured distance d 211and the angle θ 212. The decision unit 202 may determine the loadimpedance such that a maximum power may be transmitted from a wirelesspower transmission device (not shown) to a terminal (not shown). Ascheme for determining the load impedance is described with reference toFIG. 3.

FIG. 3 illustrates an example of a Z-matrix of a load impedance Z_(L), asource resonator, and a target resonator.

Referring to FIG. 3, a configuration 310 of source resonator 311, targetresonator 312, and load impedance Z_(L) 313 is illustrated. The sourceresonator 311 and the target resonator 312 are separated from each otherby a distance d 315 and an angle θ 316. The target resonator 312 isconnected to the load impedance Z_(L) 313.

Z_(in) 314 denotes an input impedance viewed from a wireless powertransmission device (not shown) that supplies power.

FIG. 3 also illustrates Z matrix 320 with respect to the configuration310. Z₁₁ corresponds to an impedance of the source resonator 311, Z₁₂corresponds to an impedance between the source resonator 311 and thetarget resonator 312, and Z₂₂ corresponds to an impedance of the targetresonator 312,

A scheme for determining the load impedance such that a maximum powermay be transmitted from the wireless power transmission device to theterminal is described herein.

The input impedance Z_(in) 314 may be determined using the followingEquation 1:

$\begin{matrix}{{Z_{k} = {Z_{22} - Z_{12} + Z_{L}}}{Z_{n} = {{{Z_{12}//\left. Z_{k}\rightarrow\begin{matrix}{\frac{1}{Z_{n}} = {\frac{1}{Z_{12}} + \frac{1}{Z_{k}}}} \\{= {\frac{1}{Z_{12}} + \frac{1}{Z_{22} - Z_{12} + Z_{L}}}} \\{= \frac{Z_{22} + Z_{L}}{Z_{12}\left( {Z_{22} - Z_{12} + Z_{L}} \right)}}\end{matrix} \right.}\therefore Z_{n}} = {Z_{12} - \frac{Z_{12}^{2}}{Z_{22} + Z_{L}}}}}{Z_{in} = {{Z_{11} - Z_{12} + Z_{n}} = {Z_{11} - {\frac{Z_{12}^{2}}{Z_{22} + Z_{L}}.}}}}} & (1)\end{matrix}$

In this example, Z_(k) corresponds to a sum of impedances included in adotted circle 321, and Z_(n) corresponds to a sum of impedances includedin a dotted circle 322.

An input power P_(in) supplied by the wireless power transmission devicemay be expressed by the following Equation 2:

$\begin{matrix}{P_{in} = {\frac{1}{2}{{{Re}\left\lbrack Z_{in} \right\rbrack} \cdot {{I_{in}}^{2}.}}}} & (2)\end{matrix}$

In this example, I_(in) corresponds to a current flowing from thewireless power transmission device that supplies power in the Z matrix.

Power P_(L) transferred to a load from among the input power P_(in)supplied by the wireless power transmission device, may be expressed bythe following Equation 3:

$\begin{matrix}\begin{matrix}{P_{L} = {\frac{1}{2}{{{Re}\left\lbrack Z_{L} \right\rbrack} \cdot {I_{L}}^{2}}}} \\{= {\frac{1}{2}{{{Re}\left\lbrack Z_{L} \right\rbrack} \cdot {\frac{Z_{12}I_{in}}{Z_{k} + Z_{12}}}^{2}}}} \\{= {\frac{1}{2}{{{Re}\left\lbrack Z_{L} \right\rbrack} \cdot {{\frac{Z_{12}I_{in}}{Z_{22} + Z_{L}}}^{2}.}}}}\end{matrix} & (3)\end{matrix}$

Based on Equation 2 and Equation 3, a power transfer efficiency PTE maybe expressed by the following Equation 4:

$\begin{matrix}{{PTE} = {\frac{P_{L}}{P_{in}} = {\frac{{Re}\left\lbrack Z_{L} \right\rbrack}{{Re}\left\lbrack Z_{in} \right\rbrack} \cdot {{\frac{Z_{12}}{Z_{22} + Z_{L}}}^{2}.}}}} & (4)\end{matrix}$

The load impedance Z_(L) to transmit the maximum power may be determinedusing the following Equation 5:

$\begin{matrix}{\quad\left\{ \begin{matrix}{\frac{\partial{PTE}}{\partial{{Re}\left\lbrack Z_{L} \right\rbrack}} = 0} \\{\frac{\partial{PTE}}{\partial{{Im}\left\lbrack Z_{L} \right\rbrack}} = 0.}\end{matrix} \right.} & (5)\end{matrix}$

A load impedance Z_(L) that satisfies the above Equation 5 may beexpressed as an optimum load impedance Z_(L) ^(opt). A power transferefficiency PTE_(max) at which the optimum load impedance Z_(L) ^(opt)and the maximum power may be transmitted may be expressed by thefollowing Equation 6:

$\begin{matrix}{{{{Re}\left\lbrack Z_{L}^{opt} \right\rbrack} = {{{Re}\left\lbrack Z_{22} \right\rbrack}\sqrt{1 - {{Re}\left\lbrack X^{2} \right\rbrack} - {\frac{1}{4}{{Im}\left\lbrack X^{2} \right\rbrack}^{2}}}}}{{{Im}\left\lbrack Z_{L}^{opt} \right\rbrack} = {{\frac{1}{2}{{{Re}\left\lbrack Z_{22} \right\rbrack} \cdot {{Im}\left\lbrack X^{2} \right\rbrack}}} - {{Im}\left\lbrack Z_{22} \right\rbrack}}}{{PTE}^{\max} = {\frac{{X}^{2}}{2 - {{Re}\left\lbrack X^{2} \right\rbrack} + \sqrt{{4\left( {1 - {{Re}\left\lbrack X^{2} \right\rbrack}} \right)} - {{Im}\left\lbrack X^{2} \right\rbrack}^{2}}}.}}} & (6)\end{matrix}$

In the above Equation 6, X may correspond to the following Equation 7:

$\begin{matrix}{{{\begin{matrix}{X = {\frac{Z_{12}}{{Re}\left\lbrack Z_{22} \right\rbrack} = \frac{R_{a\; 1}^{rad}{T}\sqrt{\frac{{Re}\left\lbrack Z_{22} \right\rbrack}{{Re}\left\lbrack Z_{11} \right\rbrack}}}{{Re}\left\lbrack Z_{22} \right\rbrack}}} \\{= {{R_{a\; 1}^{rad}{T}\frac{1}{\sqrt{{{Re}\left\lbrack Z_{11} \right\rbrack} \cdot {{Re}\left\lbrack Z_{22} \right\rbrack}}}} = {\frac{R_{a\; 1}^{rad}{T}}{{Re}\left\lbrack Z_{11} \right\rbrack}\sqrt{\frac{{Re}\left\lbrack Z_{11} \right\rbrack}{{Re}\left\lbrack Z_{22} \right\rbrack}}}}}\end{matrix}\therefore X} = \left. {\eta_{{eff\_}1}T\sqrt{\frac{{Re}\left\lbrack Z_{11} \right\rbrack}{{Re}\left\lbrack Z_{22} \right\rbrack}}}\Leftarrow\left( {{\because\eta_{{eff\_}1}} = \frac{R_{a\; 1}^{rad}}{{Re}\left\lbrack Z_{11} \right\rbrack}} \right) \right.}{T = {\frac{3}{2}\left\{ {{{- \sin^{2}}\theta\frac{1}{j\;{kd}}} + {\left( {{3\;\cos^{2}\theta} - 1} \right)\left\lbrack {\frac{1}{\left( {j\;{kd}} \right)^{2}} + \frac{1}{\left( {j\;{kd}} \right)^{3}}} \right\rbrack}} \right\}{{\mathbb{e}}^{{- j}\;{kd}}.}}}} & (7)\end{matrix}$

In this example, d corresponds to the distance d 315 between the sourceresonator 311 and the target resonator 312, and θ corresponds to theangle θ 316 between the source resonator 311 and the target resonator312.

As an example, a measurement unit of the load impedance decision unitmay measure the distance d 315 and the angle θ 316 between the sourceresonator 311 and the target resonator 312, and the decision unit maydetermine a load impedance based on at least one of the measureddistance d 315 and the angle θ 316 such that the maximum power may betransmitted as shown in the above Equation 6.

FIG. 4 illustrates an example of a wireless power transmission device.

Referring to FIG. 4, wireless power transmission device 400 includes aload impedance decision unit 410 and a change unit 420. The loadimpedance decision unit 410 includes a measurement unit 411 and adecision unit 412. The measurement unit 411 may measure at least one ofa distance and an angle between a source resonator and a targetresonator. The decision unit 412 may determine a load impedance based onat least one of the measured distance and angle.

Descriptions related to the load impedance decision device made withreference to FIGS. 2 and 3 may be applicable to the load impedancedecision unit 410. Accordingly, further descriptions related thereto areomitted here.

The change unit 420 may change an impedance of the wireless powertransmission device 400 to be conjugated with the load impedancedetermined by the load impedance decision unit 410, for example, thechange unit 420 may change the impedance of the wireless powertransmission device and combine the load impedance determined by theload impedance decision unit 410 with the impedance of the wirelesspower transmission device 400. For example, the change unit 420 maychange the impedance of the wireless power transmission device 400 basedon a tunable resistance, an inductor, a capacitor, a combinationthereof, and the like.

The wireless power transmission device 400 may include a testing unit450 and a control unit 440. The testing unit 450 may transmit a testpower using the changed impedance. An amount of the test power may bepredetermined, or it may be input from an outside source.

For example, when a power transfer efficiency of the test power is lessthan or equal to a reference value, the control unit 440 may control theload impedance decision unit 410 to re-determine the load impedance. Asanother example, when the power transfer efficiency of the test power isgreater than or equal to the reference value, the control unit 440 maycontrol the wireless power transmission device 400 to wirelesslytransmit power using the changed impedance. For example, the referencevalue may be predetermined or may be input from an outside source. Asanother example, when the power transfer efficiency of the test power isless than the reference value, the control unit 440 may suspend atransmission of the test power.

For example, a power transfer efficiency may be determined by measuringa power of a reflected wave that reflects from the target resonator inresponse to receiving a transmission signal. The transmission signalcorresponds to a signal to wirelessly transmit power from a sourceresonator to a target resonator. The reflected wave corresponds to aportion of the transmission signal that is reflected and is returned.

For example, when the power of the reflected wave is less than or equalto a reference value, this may indicate that a significant portion ofthe power transmitted to the target resonator was received by the targetresonator. For example, when a reflected wave is less than a referencevalue, this may correspond to a case where the power transfer efficiencyis greater than or equal to the reference value. Accordingly, thecontrol unit 440 may control the wireless power transmission device 400to wirelessly transmit the power using the changed impedance.

Conversely, when the power of the reflected power is greater than thereference value, this may indicate that only a small amount of powertransmitted to the target resonator was received by the targetresonator. For example, when a reflected wave is greater than areference value, this may correspond to a case where the power transferefficiency is less than the reference value. Accordingly, the controlunit 440 may control the load impedance decision unit 410 tore-determine the load impedance. For example, the control unit 440 mayinclude a power detector (not shown) to measure the power of thereflected wave, and may measure the power of the reflected wave usingthe power detector.

For example, the power transfer efficiency may be determined bymeasuring an amplitude of the reflected wave. For example, when theamplitude of the reflected wave is less than or equal to the referencevalue, this may indicate that only a small amount of power was reflectedand a significant portion of the power was received by the targetresonator. Accordingly, the control unit 440 may control the wirelesspower transmission device 400 to wirelessly transmit the power using thechanged impedance.

Conversely, where the amplitude of the reflected power is greater thanthe reference value, this may indicate that a significant portion of thepower was reflected and only a small amount of power was received by thetarget resonator. Accordingly, the control unit 440 may control the loadimpedance decision unit 410 to re-determine the load impedance.

The wireless power transmission device 400 may include a transmitter430. The transmitter 430 may transmit, to a terminal (not shown),information associated with the load impedance that is determined by theload impedance decision unit 410. Because the transmitter 430 transmitsinformation associated with the determined load impedance to theterminal, the terminal may change an impedance of the terminal to matchthe determined load impedance.

FIG. 5 illustrates an example of a terminal that wirelessly receivespower.

Referring to FIG. 5, terminal 500 includes a load impedance decisionunit 510 and a change unit 520. The load impedance decision unit 510includes a measurement unit 511 and a decision unit 512.

The measurement unit 511 may measure at least one of a distance and anangle between a source resonator (not shown) and a target resonator (notshown). The decision unit 512 may determine a load impedance based on atleast one of the measured distance and angle.

Descriptions related to the load impedance decision device made withreference to FIGS. 2 and 3 may be applicable to the load impedancedecision unit 510. Accordingly, further descriptions related thereto areomitted here.

The change unit 520 may change an impedance of the terminal 500 to matchthe load impedance determined by the load impedance decision unit 510.For example, the change unit 520 may change the impedance of theterminal 500 based on a tunable resistance, an inductor, a capacitor, acombination thereof, and the like.

The terminal 500 may include a signal transmitter 540 and a control unit550. When the change unit 520 changes the impedance of the terminal 500,the signal transmitter 540 may transmit a test power request signal to awireless power transmission device (not shown). The amount of the testpower may be predetermined or may be input from an outside source.

When power transfer efficiency of the test power is less than areference value, the control unit 550 may control the load impedancedecision unit 510 to re-determine the load impedance. When the powertransfer efficiency of the test power is greater than or equal to thereference value, the control unit 550 may transmit a signal to awireless power transmission device to wirelessly transmit the power. Thereference value may be predetermined or may be input from an outsidesource. When the power transfer efficiency of the test power is lessthan the reference value, the control unit 550 may control the signaltransmitter 540 to transmit a signal suspending the transmission of thetest power.

The terminal 500 may include a transmitter 530. The transmitter 530 maytransmit, to the wireless power transmission device, informationassociated with the load impedance determined by the load impedancedecision unit 510. Because the transmitter 530 transmits informationassociated with the determined load impedance to the wireless powertransmission device, the wireless power transmission device may changean impedance of the wireless power transmission device to be conjugatedwith the determined load impedance.

FIG. 6 illustrates an example of a method for determining a loadimpedance.

In 610, at least one of a distance and an angle between a sourceresonator and a target resonator is measured. For example, the distancebetween the source resonator and the target resonator may be measured bya distance sensor based on light waves and/or ultrasonic waves. Theangle may indicate an angle at which the target resonator is locatedbased on the source resonator.

In 620, a load impedance is determined based on at least one of themeasured distance and angle. For example, the load impedance may bedetermined such that a maximum power may be transmitted from a wirelesspower transmission device to a terminal. A scheme for determining theload impedance is described above with reference to FIG. 3 and thusfurther description is omitted here.

FIG. 7 illustrates an example of a method for wirelessly transmittingpower.

In 710, a load impedance is determined. A scheme for determining theload impedance is described above with reference to FIGS. 2 and 3 andthus further description is omitted here.

In 720, an impedance is changed to be conjugated with the determinedload impedance. For example, the impedance may be changed based on atunable resistance, an inductor, a capacitor, a combination thereof, andthe like.

Although not shown in FIG. 7, the wireless power transmission method mayfurther include transmitting a test power and controlling powertransmission. In this example, the test power may be transmitted usingthe changed impedance. An amount of test power may be predetermined ormay be input from an outside source.

When a power transfer efficiency of the test power is less than areference value, the load impedance may be controlled to bere-determined. When the power transfer efficiency of the test power isgreater than or equal to the reference value, a power may be controlledto be wirelessly transmitted using the changed impedance. The referencevalue may be predetermined or may be input from an outside source. Whenthe power transfer efficiency of the test power is less than thereference value, a transmission of the test power may be suspended.

For example, a power transfer efficiency may be determined by measuringa power of a reflected wave that reflects in response to thetransmission signal. The transmission signal corresponds to a signal towirelessly transmit power from a source resonator to a target resonator.The reflected wave corresponds to a portion of the transmission signalthat is reflected and returned.

For example, when the power of the reflected wave is less than or equalto a reference value, this may indicate that only a small amount ofpower was reflected and a significant portion of the power transmittedto the target resonator was received by the target resonator. Forexample, it may correspond to a case where the power transfer efficiencyis greater than or equal to the reference value. Accordingly, the powermay be controlled to be wirelessly transmitted using the changedimpedance.

Conversely, when the power of the reflected power is greater than thereference value, this may indicate that a significant portion of thepower was reflected and only a small amount of power transmitted to thetarget resonator is received by the target resonator. For example, itmay correspond to a case where the power transfer efficiency is lessthan the reference value. Accordingly, the load impedance may becontrolled to be re-determined. For example, the wireless powertransmission method may measure the power of the reflected wave using apower detector configured to measure the power of the reflected wave.

Accordingly, based on the measured power of the reflective wave, thewireless power transmission device may determine to adjust the amount ofpower transmitted to a wireless power receiving device. For example, thewireless power transmission device may adjust the load impedance totransfer a more efficient amount of power.

The power transfer efficiency may be determined by measuring anamplitude of the reflected wave of the transmission signal. For example,when the amplitude of the reflected wave is less than or equal to thereference value, this may indicate that only a small amount of power wasreflected and this may indicate that a significant portion of the powertransmitted to the target resonator was received by the targetresonator. Accordingly, the power may be controlled to be wirelesslytransmitted using the changed impedance.

Conversely, when the amplitude of the reflected power is greater thanthe reference value, this may indicate that a significant portion of thepower may be reflected and only a small amount of the power transmittedto the target resonator is actually received by the target resonator.Accordingly, the load impedance may be controlled to be re-determined.

Although not shown in FIG. 7, the wireless power transmission method mayfurther include transmitting, to a terminal, information associated withthe determined load impedance. Through this, the terminal may change animpedance of the terminal to match the determined load impedance.

The processes, functions, methods, and/or software described above maybe recorded, stored, or fixed in one or more computer-readable storagemedia that includes program instructions to be implemented by a computerto cause a processor to execute or perform the program instructions. Themedia may also include, alone or in combination with the programinstructions, data files, data structures, and the like. Examples ofcomputer-readable storage media include magnetic media, such as harddisks, floppy disks, and magnetic tape; optical media such as CD ROMdisks and DVDs; magneto-optical media, such as optical disks; andhardware devices that are to specially configured to store and performprogram instructions, such as read-only memory (ROM), random accessmemory (RAM), flash memory, and the like. Examples of programinstructions include machine code, such as produced by a compiler, andfiles containing higher level code that may be executed by the computerusing an interpreter. The described hardware devices may be configuredto act as one or more software modules in order to perform theoperations and methods described above, or vice versa. In addition, acomputer-readable storage medium may be distributed among computersystems connected through a network and computer-readable codes orprogram instructions may be stored and executed in a decentralizedmanner.

As a non-exhaustive illustration only, the terminal device describedherein may refer to mobile devices such as a cellular phone, a personaldigital assistant (PDA), a digital camera, a portable game console, anMP3 player, a portable/personal multimedia player (PMP), a handhelde-book, a portable lab-top personal computer (PC), a global positioningsystem (GPS) navigation, and devices such as a desktop PC, a highdefinition television (HDTV), an optical disc player, a setup box, andthe like, capable of wireless communication or network communicationconsistent with that disclosed herein.

A computing system or a computer may include a microprocessor that iselectrically connected with a bus, a user interface, and a memorycontroller. It may further include a flash memory device. The flashmemory device may store N-bit data via the memory controller. The N-bitdata is processed or will be processed by the microprocessor and N maybe 1 or an integer greater than 1. Where the computing system orcomputer is a mobile apparatus, a battery may be additionally providedto supply operation voltage of the computing system or computer.

It should be apparent to those of ordinary skill in the art that thecomputing system or computer may further include an application chipset,a camera image processor (CIS), a mobile Dynamic Random Access Memory(DRAM), and the like. The memory controller and the flash memory devicemay constitute a solid state drive/disk (SSD) that uses a non-volatilememory to store data.

A number of examples have been described above. Nevertheless, it shouldbe understood that various modifications may be made. For example,suitable results may be achieved if the described techniques areperformed in a different order and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner and/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

1. A load impedance decision device comprising: a measurement unitconfigured to measure at least one of a distance and an angle between asource resonator and a target resonator; and a decision unit configuredto determine the load impedance based on at least one of the measureddistance and the measured angle; wherein the source resonator isconfigured to transmit resonant power to the target resonator based onthe load impedance that is determined based on at least one of themeasured distance and the measured angle.
 2. The load impedance decisiondevice of claim 1, wherein the decision unit is configured to determinethe load impedance based on both the measured distance and the measuredangle.
 3. The load impedance decision device of claim 1, wherein theload impedance decision unit is included in the source resonator, andthe measured angle corresponds to an angle with which the sourceresonator is tilted with respect to the target resonator.
 4. A wirelesspower transmission device comprising: a load impedance decision unit;and a change unit configured to change an impedance of the wirelesspower transmission device to be conjugated with a load impedancedetermined by the load impedance decision unit, wherein the loadimpedance decision unit comprises a measurement unit configured tomeasure at least one of a distance and an angle between a sourceresonator of the wireless power transmission device and a targetresonator, and a decision unit configured to determine the loadimpedance based on at least one of the measured distance and themeasured angle, and the source resonator is configured to transmitresonant power to the target resonator based on the load impedance thatis determined based on at least one of the measured distance and themeasured angle.
 5. The wireless power transmission device of claim 4,further comprising: a transmitter configured to transmit, to a terminal,information associated with the load impedance determined by the loadimpedance decision unit.
 6. The wireless power transmission device ofclaim 4, wherein the change unit is configured to change the impedanceof the wireless power transmission device based on at least one of atunable resistance, an inductor, and a capacitor.
 7. The wireless powertransmission device of claim 4, further comprising: a testing unitconfigured to transmit a test power using the changed impedance; and acontrol unit configured to control the load impedance decision unit tore-determine the load impedance when a power transfer efficiency of thetest power is less than a reference value, and to control the wirelesspower transmission device to wirelessly transmit a power using thechanged impedance when the power transfer efficiency of the test poweris greater than or equal to the reference value.
 8. The wireless powertransmission device of claim 4, wherein the decision unit is configuredto determine the load impedance based on both the measured distance andthe measured angle.
 9. The wireless power transmission device of claim4, wherein the wireless power transmission device includes a sourceresonator, and the measured angle corresponds to an angle with which thesource resonator is tilted with respect to the target resonator.
 10. Aterminal to wirelessly transmit power, the terminal comprising: a loadimpedance decision unit; and a change unit configured to change animpedance of the terminal to match a load impedance determined by theload impedance decision unit, wherein the load impedance decision unitcomprises a measurement unit configured to measure at least one of adistance and an angle between a source resonator of the terminal and atarget resonator, and a decision unit configured to determine the loadimpedance based on at least one of the measured distance and themeasured angle, and the source resonator is configured to transmitresonant power to the target resonator based on the load impedance thatis determined based on at least one of the measured distance and themeasured angle.
 11. The terminal of claim 10, further comprising: atransmitter configured to transmit, to a wireless power transmissiondevice, information associated with the load impedance determined by theload impedance decision unit.
 12. The terminal of claim 10, wherein thechange unit change is configured to change the impedance of the terminalbased on at least one of a tunable resistance, an inductor, and acapacitor.
 13. The terminal of claim 10, further comprising: a signaltransmitter configured to transmit a test power request signal to awireless power transmission device when the change unit changes theimpedance of the terminal; and a control unit configured to control theload impedance decision unit to re-determine the load impedance when apower transfer efficiency of the test power is less than a referencevalue, and to transmit a signal to the wireless power transmissiondevice to wirelessly transmit power when the power transfer efficiencyof the test power is greater than or equal to the reference value. 14.The terminal of claim 10, wherein the decision unit is configured todetermine the load impedance based on both the measured distance and themeasured angle.
 15. The terminal of claim 10, wherein the terminalincludes a source resonator, and the measured angle corresponds to anangle with which the source resonator is tilted with respect to thetarget resonator.
 16. A method to determine a load impedance, the methodcomprising: measuring at least one of a distance and an angle between asource resonator and a target resonator; and determining the loadimpedance based on at least one of the measured distance and themeasured angle, wherein the source resonator is configured to transmitresonant power to the target resonator based on the load impedance thatis determined based on at least one of the measured distance and themeasured angle.
 17. The method of claim 16, wherein the load impedanceis determined based on both the measured distance and the measuredangle.
 18. The method of claim 16, wherein the measured anglecorresponds to an angle with which the source resonator is tilted withrespect to the target resonator.
 19. A method to wirelessly transmitpower, the method comprising: determining a load impedance; and changingan impedance to be conjugated with the determined load impedance,wherein the determining comprises measuring at least one of a distanceand an angle between a source resonator and a target resonator, anddetermining the load impedance based on at least one of the measureddistance and the measured angle, and the source resonator is configuredto transmit resonant power to the target resonator based on the loadimpedance that is determined based on at least one of the measureddistance and the measured angle.
 20. A wireless power reception device,comprising: a target resonator configured to wirelessly receive resonantpower transmitted from a source resonator of a wireless powertransmission device; and a load that is charged by the resonant powerthat is wirelessly received, wherein the resonant power transmitted fromthe source resonator is based on a load impedance that is determinedbased on at least one of a measured distance and a measured anglebetween the source resonator and the target resonator.